.Net’s using() for Java

admin — Wed, 11 Nov 2009 19:22:38 +0000

As I'm working as a Java developer in a microsoft oriented company this means I sometime have to do .Net programming.
As there are some things I don't like about .Net (no checked exceptions is one) there is one thing I find very good and useful.

In .Net an object that implements the IDisposable interface can be initiated with the Using command like this:

using (TextWriter w = File.CreateText("log.txt"))
    { w.WriteLine("This is line one");
}

After the block has executed, using will take care of closing the writer and freeing the resources.
This gives me solid readable code without memoryleaks.

Now looking at Java, closing resources usually involves putting a close() in a finally block, with another try-catch construction to catch exceptions that the close() can throw.
this is ugly, errorprone and can obfuscate the real exception that happened.

Java 7 comes to the rescue, one of the approved proposals for java 7 is "automatic resource management"
the following code block will demonstrate this

static void copy(String src, String dest) throws IOException {
   try (InputStream in = new FileInputStream(src); 
         OutputStream out = new FileOutputStream(dest)) {
 
        byte[] buf = new byte[8192];
        int n;
        while ((n = in.read(buf)) >= 0)
        out.write(buf, 0, n);
    }
    //optional catch block
    //optional finally block
}

In Java 6 or lower the above code would contain 2 try-finally blocks to handle closing the input and ouput streams, another 2 try-catch blocks to handle exceptions from the close() commands, and more catches for exceptions you would want to handle specifically

Off all the features in java 7 this is the one I'm looking forward the most, the forkjoin and invokeDynamic changes following close though.
here is a list of all the features in java 7
http://openjdk.java.net/projects/jdk7/features/

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.Net’s using() for Java